1. Field of the Invention:
An important factor in laying pipelines composed of a number of individual sections is how uniformly the ends of each section are cut. It is desirable that the pipe ends be as close to perpendicular to the pipe axis as possible so that when the sections are laid end-to-end the line will be straight. The American Petroleum Institute (API) has promulgated specifications 5L (Paragraph 7.3) and 5LX (Paragraph 6.7) which require that, "for pipe sizes 103/4 inches and larger, the ends shall be cut square within 1/16 inch, measured not less than three times per eight hour working shift". The term squareness refers to the plane of the pipe end being at right angles with respect to the axis, where the axis is the straight line through centerpoints of the pipe ends.
2. Prior Art:
No particular method of measurement is required in the API specifications. One method sometimes used is to place one leg of a carpenter's square along the top wall of the pipe, and measure the space between the other leg and the end of the pipe. Several readings are taken as the pipe is rolled along the floor so that the maximum deviation from squareness is determined. It is apparent that this method is subject to inaccuracies, many of which are due to curved pipe surfaces such as on pipe that is wavy or has hooked ends. Variations in the pipe diameter can also effect the readings. The method has another disadvantage in that it is time consuming since pipe must be removed individually from storage racks and placed on the floor for making the squareness determinations.
Another method of measurement sometimes used, is to place a pipe in the machine for facing the pipe ends, and mount a dial indicator in the tool holder of the machine. By rotating the pipe one full turn, (or the toolholder, if the pipe does not rotate) the reading on the dial indicates the theoretical deviation from squareness of the pipe end. The accuracy of this method is also affected by the degree of straightness of the pipe, and how it is mounted in the machine. This method also reduces productivity on the facing machines and is not desirable.